#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 510;
int n, m;
int g[N][N];
int dist[N];
bool st[N];

int dijkstra()
{
    memset(dist, 0x3f, sizeof(dist));
    dist[1] = 0;
    for (int i = 0; i < n - 1; ++i)
    {
        int t = -1;
        for (int j = 1; j <= n; ++j)
        {
            if (!st[j] && (t == - 1 || dist[t] > dist[j]))
            {
                t = j;
            }
        }
        st[t] = true;
        for (int j = 1; j <= n; ++j)
        {
            dist[j] = min(dist[j], dist[t] + g[t][j]);
        }
    }
    if (dist[n] == 0x3f3f3f3f)
    {
        return -1;
    }
    return dist[n];
}

int main()
{
    cin >> n >> m;
    memset(g, 0x3f, sizeof(g));
    while (m--)
    {
        int a, b, c;
        scanf("%d %d %d", &a, &b, &c);
        g[a][b] = min(g[a][b], c);
    }
    printf("%d", dijkstra());
    return 0;
}